Because your essay must be three paragraphs, I would write the thesis statement as a topic sentence or as a lead-in sentence. In your thesis statement, include what you think were the major effects of the Age of Exploration on Africa, particularly West Africa, and the Americas.
In the Americas, the major effects of the Age of Exploration were disease and displacement. The natives in North and South America were unable to resist the diseases that Europeans were carrying, particularly yellow fever, influenza, and smallpox. This resulted in the decimation of large swathes of the native populations. Those who survived were subjected to displacement, due to European settlement. Having to leave their homes was devastating to many natives, and some were unable to survive in new environments.
In the Caribbean, Native Americans were enslaved. Initially, the Spanish -- the first to arrive -- sought gold. They forced the natives to labor in the mines. Those who refused were murdered; others were forced to starve after the Spanish destroyed their crops in retaliation for their resistance. Others simply died from exhaustion. Mining is taxing work, especially when one is forced to do it for excessively long hours in tropical heat.
The need for laborers who could work in tropical climates caused European traders and planters to look toward West Africa. The first African slaves were introduced into Hispaniola (what is now Haiti and the Dominican Republic) by the Spanish in 1501, nine years after Columbus's arrival in the West Indies.
According to C.L.R. James, Central Africa (e.g., the Congo) "was a territory of peace and happy civilization" in the sixteenth century, shortly before the arrival of European traders. As far as we know, the same could be said of the Americas before the arrival of Spanish and Portuguese traders, starting in the late fifteenth century.
Like the Native Americans, Africans greeted the Europeans hospitably. As in the Americas, tribal life was broken up due to displacement and enslavement. Also, crops were destroyed by traders in Africa, just as they were in the Americas, leading to famine.
According to James, tribes had to provide the Europeans with slaves or be sold as slaves themselves. In exchange for providing slaves, they would receive guns and sums of gold or silver. It is true that slavery existed in West Africa prior to the arrival of Europeans. Slavery was also practiced among some Native American tribes. In Africa, however, the system was more akin to apprenticeship. Also, a slave did not remain a slave for an entire lifetime, and physical cruelty was not practiced. Those who try to draw parallels between these systems and that which existed in the Americas, after European settlement, are wrong.
Clearly, the motivation for the European traders and planters was economic. They wanted laborers who could mine and till the lands they had colonized. They also needed laborers who could withstand the tropical climate. Because they wanted to reap maximum profits, they chose to enslave people. They justified their actions by associating Africans and Native Americans with heathenism, or non-Christian belief systems. Later, when Africans and their descendants became the sole source of slave labor, skin color became the marker of the servant class.
The results of Europeans' abuses were similar in both the Americas and Africa: tribes were disbanded, populations were decimated due to famine, and peace became a distant memory.